1. Field of the Invention
The present invention relates to a seek operation of an optical disk device recording information on or reproducing information from an optical disk using an optical pick-up.
2. Description of the Background Art
Conventionally, an optical disk device has been known, which records and/or reproduces information on an optical disk having information tracks formed in concentric or spiral manner such as a CD or a DVD, using an optical head referred to as an optical pick-up. The optical pick-up is configured to emit a light beam such as a beam of a semiconductor laser to be focused through an objective lens on the optical disk, and to receive the light incident on and reflected from the optical disk to output a corresponding electric signal, and the optical pick-up moves along the radial direction of the optical disk.
The optical disk device moves the optical pick-up to a prescribed position on the optical disk, and while the optical disk rotates, light from the optical pick-up is directed and focused on a recording track of the optical disk, so that the information is recorded on and/or reproduced from the optical disk.
When information is to be reproduced from an optical disk, first, a focus-on operation (focusing) is done so that beams emitted from the optical pick-up meet on a position of an optical disk surface, and then a track-on operation (tracking) is done so that the focused light beam is positioned on a recording track. These focusing and tracking operations are realized by moving an objective lens in a direction perpendicular to the optical disk surface and a direction perpendicular to the recording track, in accordance with an electric signal output from the optical pick-up. From the electric signal output from the optical pick-up in the focused-on and tracked-on state, pits formed on the optical disk are read and the information thereof is reproduced. As to the recording of information on the optical disk, information is recorded by forming a pit or pits on the recording track of the optical disk by the light directed and focused from the optical head to the optical disk.
Prior to the reproduction and recording of information from/to the optical disk, a seek operation of moving the optical pick-up to a target track on the disk takes place.
The seek operation includes a coarse seek operation in which the optical pick-up is moved by a motor and accelerated in the direction to the target track for rough tracking around the target track as a temporal measure, followed by a fine seek operation in which the optical pick-up finely tracks the target track.
By way of example, Japanese Patent Laying-Open Nos. 08-124177, 2005-018873 and 2005-216332 propose various methods of the seek operation. A method of realizing highly accurate seek operation by controlling speed of the optical pick-up during a seek operation, for example, has been disclosed.
The method of controlling the speed of optical pick-up during a seek operation, however, involves real-time monitoring of the speed of traversing tracks and the number of traversed tracks and measurement of a difference between the target speed and the actual speed, and the motor is driven based on the result of measurement. Therefore, circuit structure becomes complicated, naturally resulting in high cost.
Further, as the speed of traversing tracks and the number of traversed tracks must be monitored during a seek operation, it is necessary to almost fully generate a tracking error signal, and hence, there is a limit on the driving speed of the motor.
Further, as it is necessary to attain track-on (tracking) during the seek operation, the tracking lens may shift while the optical pick-up is being moved by the motor, which may lead to lower sensitivity at the time of track-on (tracking), degradation of the tracking error signal or imbalanced tracking error signal, possibly resulting in a failure of track-on.